A cam indexer looks like a sealed gearbox with a shaft sticking out, but it is the timing heart of any rotary dial machine, assembly turntable, or packaging line. Pick the wrong station count, dwell angle, or input torque and the turntable either stops late, jolts the fixtures, or burns the servo motor on the first shift. A packaging engineer in Suzhou once spent three months tuning a 6-station dial because the cam indexer they bought had a dwell angle too short for the heat-station cycle; the part indexer itself was fine, the curve was wrong for the job. This guide walks an automation integrator, a packaging machine builder, or an end-user upgrading a manual dial through six checks to run before you order a cam indexer: station count, dwell angle, input torque, flange load, indexing accuracy, and mounting style. Run them in order and the unit you receive will cycle through your stations on time, not after a round of field modifications.
1. Stop Positions and Station Count
This is the first decision and it constrains everything downstream. A cam indexer comes in standard station counts of 2, 3, 4, 6, 8, 12, and 16; custom counts are possible but they cost tooling money. Count your actual workstations: load, unload, two assembly stations, a leak test, a vision check, a labeling station. If you need 7 stations, do not force an 8-station unit and leave one station empty forever; the indexer will rotate through 8 stops anyway, wasting cycle time. A cam indexer with 6 stations on a 5-station machine leaves the dial idling through one empty index each cycle, which adds 15 percent to the cycle time for free. Plan the dial layout on paper first: load and unload stations should sit across from each other to balance the moment, and heavy stations should sit near the center to keep the overhang low.
2. Dwell Angle and Cam Curve
Dwell angle is the fraction of the input revolution the output shaft stays still while the next station does its work. A 90-degree index with a 270-degree dwell means the turntable rotates in a quarter turn and holds for three quarters; a 120-degree index with a 240-degree dwell moves faster but holds less. Match the dwell to the longest station cycle: if the leak test takes 4 seconds and the index takes 1 second, you need a dwell of at least 4 times the index time. The curve itself matters too: modified sine curves start and stop smoothly, while trapezoidal curves move faster but shake heavier loads. A cam indexer with the wrong curve on a heavy turntable will rattle the fixtures loose in a month. Ask the supplier for the acceleration profile at your cycle time; a curve that peaks at 2 g is fine for light tooling but will shake a 200 kg dial off its feet.
3. Input Torque and Motor Match
The cam indexer needs an input torque to accelerate the turntable, the tooling, and the products sitting on it. Work out the total inertia on the output shaft first, then ask the supplier for the required input torque at your cycle time. A 0.75 kW servo motor sounds generous until you hang a 200 kg steel plate on the flange and ask it to index in 0.5 seconds; the torque number on the catalog is for a light, empty table, not your loaded dial. A cam indexer that stalls on the first cycle because the servo was undersized is the most expensive mistake in this list, because the motor, the drives, and the tuning all have to be redone.
4. Flange Size and Load Capacity
The output flange carries the turntable itself, the tooling, and the parts. Check the catalog for the allowed overhang load and the allowed moment load at the mounting face; a thin turntable bolted far from the bearing centerline creates a moment load that the unit was not designed for. If your turntable is 800 mm in diameter and carries 20 kg at the rim, the moment is far higher than 20 kg at the center. A cam indexer with a 300 mm center height and a flange rated for 50 Nm will leak or wear out the cam followers in six months if you overhang the load. If the turntable must be thin and wide, add a support bearing at the rim so the unit only sees the weight, not the bending moment.
5. Indexing Accuracy
Indexing accuracy is the repeatability of each stop, quoted in arc-seconds or arc-minutes. General assembly machines hold 30 to 60 arc-seconds; vision-guided stations and precision press fits need 15 to 20 arc-seconds. Ask whether the number is a unidirectional repeat or bidirectional, and whether it is tested at the rated load or empty. A cam indexer quoted at 30 arc-seconds empty that drifts to 90 arc-seconds under load is not accurate enough for a press-fit station.
6. Mounting Style and Customization
Cam indexers ship with shaft output, hollow bore output, or flange output. Shaft output is the most flexible but needs a coupling and a bearing support for the turntable; hollow bore lets the turntable sit directly on the output shaft with no coupling; flange output bolts the dial to the face. If your cycle needs a non-standard curve, ask for a custom cam grind; modified sine and modified trapezoid are standard, but a rise-dwell-fall-dwell profile for a special application costs extra tooling. A cam indexer chosen for a shaft output when the machine was designed for hollow bore will not fit the existing foot print.
Run these six checks and the cam indexer you order will match your station count, your longest cycle, your loaded turntable, and your accuracy requirement. Start with station count and dwell angle, then work out the input torque and load moment before you compare price. For related background, read our cam driven indexer article and our servo motor drive guide before you shortlist; when the quotes come back, cross-check the model selection in our micro cam splitter article and the supplier evaluation in our precision machining services guide, so the first install does not turn into a rework order.